A-Kon is already next month and I STILL don't know who I want to be...I know I was a female and someone I can pass for without having a wig on. So it'll have to be someone with dark brown hair and medium to long hair.

That's a pretty broad range, good for you C:. There's Korra, Lust, Kurenai, Lady Arachne, Soi Fong, Hinamori, Nanao Ise, Maho (Beck), Saeko (HOTD), Rei (HOTD), Fuu, Kayko (YYH), Kikyo, Kagome, Sango, most of the Azumanga Daioh characters, Haruhi, Ranma-girl, Akane (Ranma 1/2 also), Tohru, May (Pokemon), Hungary, Yuko (xxxholic)--Just naming the ones off the top of my head, but the point if, if those are the only specifications you have, you got a lot of options